Chimera is our next generation molecular graphics application whose main design goals are extensibility and ease of use. Chimera is being written in C++ and uses commonly accepted specifications such as X Windows, MOTIF and OpenInventor. In addition, Chimera also use the locally developed Object Technology Framework. Because extensibility is a major design goal, we chose to use a complete programming language, Python, as the Chimera command language. Python is an interpreted language with an extensive library that includes an interface to MOTIF. The first Chimera prototype was implemented with a small set of core functionality, including graphical display, PDB input, and basic user interface elements (menu bars, tool bar, command line, reply window and status line). More advanced features were constructed on top of the core using Python extension modules. For example, a Kinemage viewer was added, where the graphics are displayed in the main Chimera window and the textual data are displayed in a separate panel; a tool box containing icons representing Python scripts was written, all in Python; and, finally, simple script for coloring atoms and changing graphical representations were added to the tool bar, again written in Python. The first Chimera prototype was demonstrated to our advisory committee, at our departmental retreat and at the Pacific Symposium on Biocomputing and is expected to be completed in 1996.